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olorin12

Member

Registered: 2014-08-01

Posts: 18

Super slow internet while qemu VM is running

I hope this is the right place to ask this.

I've gotten GPU passthrough working in qemu - Windows 10 guest.

With no VM running, my speed test results are 25-30 mbps. With VM running, it's under 1 mbps in guest and host.
I've tried using both NAT and bridged connexion.

Any ideas?
Thanks

jsoy9pQbYVNu5nfU

Member

Registered: 2013-04-19

Posts: 108

Re: Super slow internet while qemu VM is running

For the guest: Be sure to use the VirtIO network card and the vhost_net host driver.

On the host: Unless the routing of the traffic is really broken for whatever reason, the traffic to and from the host should not flow through NAT in the first place. Please post the full and exact configuration you're using for the network setup, or the libvirt settings you're applying if you're using that. Also the full configuration of nftables or iptables. Are you using a bridge and are letting both host and VM traffic flow through it? What path is traffic taking? Is there packet loss? If yes, on which routes (mtr is good for checking this) (like host<>internet, host<>vm, vm<>host)?

In any case, the impact of NAT and bridging per se should be next to zero on networking performance.

Finally, check if the host is getting very starved for RAM/swapping all the time.

Last edited by jsoy9pQbYVNu5nfU (2019-03-03 11:14:37)

Piri

Member

Registered: 2018-06-02

Posts: 70

Re: Super slow internet while qemu VM is running

With no VM running, my speed test results are 25-30 mbps. With VM running, it's under 1 mbps in guest and host.

Have you checked the Windows Task Manager for bandwidth usage? Is Windows completely updated?
AFAIK Windows likes to do updates without limiting bandwidth usage

Head_on_a_Stick

Member

From: The Wirral

Registered: 2014-02-20

Posts: 9,003

Website

Re: Super slow internet while qemu VM is running

Any ideas?

Is there anything relevant printed to the journal when you experience this problem?

---

Jin, Jîyan, Azadî

olorin12

Member

Registered: 2014-08-01

Posts: 18

Re: Super slow internet while qemu VM is running

Thank you, sorry I was gone for a bit.

I am using the Virtio card with its driver (RedHat virtio).

"Please post the full and exact configuration you're using for the network setup, or the libvirt settings you're applying if you're using that."
I am using libvirt. Which files should I be posting here exactly?

"Also the full configuration of nftables or iptables."
Which files for that?

Using mtr doesn't show any problems.

I have 32GB RAM divided evenly between host/guest, and neither is being starved.

Just fired up the VM and am downloading things; internet speeds seem to be fine at the moment. Possibly some update to packages between then and now has fixed this? Curious.